Process for the manufacture of paper



Patented Aug. 13, 1935 raocsss Foa THE MANUFACTURE or mean Harry HuetNelson, Paris,

and Guillaume Becker,

Versailles, France No Drawing. Application April 14, 1933, Serial N0.666,224. In France April 19, 1932 -2 Claims.

The present invention relates to a process of manufacture of awaterproof paper or cloth having a high mechanical resistance especiallyin the wet state, and likewise possessing a very high 5 chemicalresistance, said paper being particularly suitable as packing paper andfor the manufacture of paper bags of the type used for example forcarrying plaster or other materials.

Said process is essentially characterized by the fact that the paperpulp, that is to say, the cellulose fibres, previously obtained by anyof the usual known means, but preferably by a chemical method andsuperficially hydrated, are impregnated with an alkaline solutionoffreshly prepared cellulose thiosulfocarbonate, which is then subjectedto the action of a suitable coagulant producing a precipitation ofhydrocellulose which constitutes the binder of the cellulose fibres.

Such coagulated hydrocellulose exists in the paper according to theinvention in a form similar to that in which it exists in artificialsilk. As such hydrocellulose has a very high tensile strength, the paperthus obtained is likewise very resistant.

If such a solution is permitted to age, its viscosity increases and itscolloidal micellae polymerize, giving rise in the space of six to eightdays to the product used in the artificial silk trade under the name ofviscose. Numerous tests have shown that it is just as impossible toobtain the desired effect with this product, when a previously formedpaper web is impregnated with it as when the paper is prepared directlyby adding the product in the pulping machine.

It would seem from the above and from observations of the phenomena ofcoagulation and regeneration of the cellulose oi the solution that inthe course of manufacture the condensation of the thiosulfocarbonate isconsiderably accelerated under the influence of the contact ot theexcess cellulose.

Coagulation may be effected by means of any of the numerous coagulantsused for viscose, subject, however, to the proviso that its acidityshall be considerably diminished as otherwise it has been found that thesudden change from the alkaline state of the thiosulfocarbonate solutionhas a harmful eil'ect on account oi the acid condition of the coagulantbath,'and destroys the homogeneousness of the fibre-binder mixture ofthepaper. It is therefore necessary to arrange matters so that .thechanges about the neutral point will be as small as possible, that is tosay that the solution to coagulate shall have the minimum of alkalinityand the coagulant the minimum of acidity necessary to render theoperation successful.

The use of coagulants having the same composition and concentration asthose used in the preparation of viscose silk would result in valuelessproducts completelyfilled with gas bubbles. A good quality of theproduct according to the present invention can only be obtained bydiminishing the quantity of bi-sulfate, or sulfuric or M hydrochloricacid etc. contained side by side with the neutral salts in thecoagulants of viscose to reduce it to or 1/20 of the usualconcentrations. Better and more reliable results are obtained if thestrong acids are replaced by weak 15 acids, as for example sulfurousacidor bi-sulfites. Another method consists in providing two 00- agulantbaths: a first saline bath having a neutral or alkaline chemicalreaction, and a second slightly acidulated bath which promotes coagula-20 tion. By slightly heating the coagulation baths their reagentconcentration may be diminished, and the qualities of the paper obtainedimproved.

The cellulose thiosulfocarbonate may be impregnated by soaking thealready formed paper in a solution of thiosulfocarbonate, it beingpossible to facilitate penetration by previously moistening the paperwith a very dilute alkaline solution of thiosulfocarbonate as also bythe vacuum producedunder the paper web if a paper couchso ing machine isused.

After coagulation, the paper is washed to rid it of impurities and thendried. To eliminate all traces of sulfur, hyposulfate or an alkalinesulfide may be added to the wash water.

There is thus obtained a translucent and homogeneous sheet of paperhaving the aspect of green leather and which, under the influence offormaldehyde, undergoes a change of appearance and quantity like leatherduring tanning. 40 Such paper is highly resistant and is particularlysuitable for the manufacture of packing sacks for building materials orsimilar applications.

The invention is likewise concerned with a process for preparing in thecold the alkaline cellulose from which the solution of cellulosethiosulfocarbonate is derived.

It is known that the viscosity of the thiosulfocarbonate solution isreduced if the alkaline cellulose serving for its manufacture isprepared 50 in the cold. This fact has not been made use of on anindustrial scale on account of the dimculties in cooling byrefrigeration a 17.5% solution of caustic soda to temperatures at whichthere is advantage in applying it. I

It has been observed that such cooling may be readily performed if asolution of caustic soda which is more concentrated than that servingfor the manufacture of alkaline cellulose is first prepared and if it isthen brought back to the desired percentage by addition of crushed ice.By mixing six parts of a lye of 30% sodium hydrate with four parts ofice, it is possible to obtain a 18% lye, the temperature of which isapproximately 25 C. lower than that of the original lye. This solutionenables the alkaline cellulose to be easily prepared industrially attemperatures below 0 C.

Another advantage of the process is that it avoids the formation ofhemicelluloses which are produced when the temperature of the reactionexceeds a certain value and which result in unusable products.

The products based on regenerated cellulose are generally softened aftercoagulation with glycerine or gluclose. Such softening effect disappearsin the wash and leaves a brittle product which has undergoneconsiderable contraction.

Such drawbacks are avoided by adding a small proportion of soap to thesolution of cellulose thiosulfocarbonate, before coagulation, soap ispreferably added in the form of a solution of soft soap, and moreparticularly in the form of resinous soap which possesses the propertyof not precipitating with hydrated lime, and as castor oil soap, whichprevents the regenerated cellulose from contracting. The soap micella:

which are too big to pass through the micellae A network of theregenerated cellulose, remain after coagulation trapped in the celluloseand leave it in its initial qualities even after a. lengthy exposure inwater. There is advantage in using mixtures of such soaps to combinetheir qualities.

Certain techincal points are involved in the impregnation of the paperdue to the colloidal nature of the cellulose thiosulfocarbonatesolution.

For the impregnation to be satisfactory, it is first of all necessary towait a few minutes between the moment when the product is applied andthe leaf coagulates. In the case of continuous manufacture, such waitingperiod is obtained by causingthe leaf to zig-zag through two rows ofrolls placed in front of the coagulation tanks. To avoid tear, the paperweb may be transported on conveyor cloths, or it may be passed roundlightly constructed drums of large diameter.

The product is applied by means of rubbercoated cylinders. There isadvantage in providing two systems of coating rollers, the first ofwhich, located forward of the impregnation track, deposits more productthan necessary, while the second removes excess after the impregnationand evens up the thickness of the leaf. In spite of all precautions, itis often impossible Such to obtain a uniform web on account of the airincluded in the starting paper web which prevents the cellulose solutionfrom penetrating. The web obtained then reveals opaque patches havingirregular forms, This may be avoided if the web of paper is slightlymoistened with water on one side, and if the moistened web is thenapplied against a heated cylinder. The contact with the cylinder causesthe water to be converted into steam, which can only escape by passingthrough the web, driving before it the air contained therein and takingits place.

If now the cold cellulosic solution be applied on both sides of the hotsteam-laden web, the sudden condensation of the steam creates a vacuumin the paper web whereby the viscose solution is drawn in and ahomogeneous impregnation is obtained.

Another means of obtaining a homogeneous impregnation consists in theuse of a perforated cylinder provided internally with cells, some ofwhich are in communication with a suction device, similarly to cellularfilters, while the cells at the points at which the paper engages withand leaves the cylinder are open to the atmosphere. The product is thenapplied by means of a coating roller to one side of the paper before itreaches the suction cylinder. While the paper passes on this cylinder,the product is drawn through all its pores and when the strip is takenofl, the other side is likewise printed and the whole equalized and theexcess removed by means of two straining rolls.

It is of course understood that the processes described herein arelikewise applicable in the same conditions and procuring the sameadvantages in order to obtain any highly resistant waterproof 'cloth ortextile material.

We claim:

1. Process of manufacture of a waterproof and highly resistant paper orcloth consisting in moistening the formed paper web with a dilutesolution of thiosulfocarbonate, in then impregnating the web with asolution offreshly prepared cellulose thiosulfocarbonate, and inprecipitating hydrocellulose constituting the binder of the cellulosefibers by means of a coagulant of viscose of weak acidity.

2. A process for the manufacture of a water proof and highly resistantpaper and the like comprising refrigerating an alkali solution, treatingcellulose with said solution to form alkaline cellulose, preparingcellulose thiosulphocarbonate from said alkaline cellulose, impregnatingthe material to be treated with a freshly prepared solution of saidcellulose thiosulphocarbonate and precipitating hydrocellulose in thematerial by means of a coagulant.

' HARRY HUET NELSON.

GUILLAUME BECKER.

